The purpose of this proposal is to further develop and maintain a pathogen free mouse colony as a resource for several departments at the University of Connecticut, and as a national resource. Many of the stocks and single gene mutations on inbred strain backgrounds in the colony are unique. They are being maintained under pathogen free conditions (1) to insure their survival; (2) to permit replication of both the genetic materials and the conditions of rearing upon which ongoing research with these animals has been based; (3) to permit genetic studies of aging to be undertaken without spurious deaths due to intercurrent disease; (4) to provide baseline populations for studies involving handling an stress, that are not contaminated by stress due to subclinical or undetected infection; and (5) to compare the results obtained with SPF mice with those obtained from identical genotypes reared conventionally on studies of stress, aging, and behavior.